1. Field of the Invention
The present invention relates to sewing machines, and in particular, to sewing machines having a drive device for moving a fabric-supporting frame in both the X-direction and the Y-direction, which is perpendicular to the X-direction.
2. Description of the Related Art
Many known drive devices for moving a fabric supporting frame include an X-drive mechanism and a Y-drive mechanism, each of which have a rotary motor, such as a pulse motor and a servo-motor, as a drive source. Therefore, a conversion mechanism is necessary to convert the rotary movement of the motor into a linear movement to move the frame in the X and Y directions. Such a motion conversion mechanism may include for example a belt and pulley mechanism, a wire and pulley mechanism or a ball-screw mechanism.
Another type of known device for moving a fabric supporting frame includes a linear motor as the drive source for the X-drive mechanism. However, the known sewing machines still require a rotary drive source and a motion conversion mechanism as the Y-drive mechanism in order to move the frame in the Y-direction. Thus, the Y-drive mechanism is the same as the above-described known devices. More specifically, the Y-drive mechanism of this type of drive device includes a belt and pulley mechanism that has a carrier mounted to a belt. The linear motor of the X-drive mechanism is supported on the carrier and has a movable member, to which a fabric supporting frame of a relatively small size is mounted. A representative example of such a sewing machine is described in Japanese Laid-Open Patent Publication No. 62-139693.
The incorporation of the motion conversion mechanism(s) complicates the construction of the drive device. In addition, due to the backlash among the mechanical parts of the motion conversion mechanism, it is difficult to improve the accuracy of the frame driving control. Although a ball-screw mechanism may be incorporated as a motion conversion mechanism to improve the accuracy of the driving control, ball-screw mechanisms are generally expensive, which can increase the manufacturing cost of the drive device.
Further, in the known drive device incorporating the linear motor as the drive source of the X-drive mechanism, the Y-drive mechanism still requires a motion conversion mechanism, which may cause backlash among the mechanical parts or may increase the manufacturing costs of producing the sewing machine with a linear motor.